Modular basal thumb joint implant

Abstract

Basal thumb joint implant has a head with a smooth, generally hemispherical, medio-proximally directed, articulating surface, and a generally abrupt, distally directed, truncation thereto; and a stem attached to the head, which arises from the truncation of the head and includes at least one of the following features:A) a general angle of attachment to the head which is acute in relation to the truncation of the head;B) a flanged cross-sectional stem profile;C) an inwardly curved stem;D) an eccentric head attachment site for the stem.The implant may be one-piece or modular in construction. The modular basal thumb joint implant, however, which is not necessarily limited by requiring inclusion of the aforesaid additional features A-D, includes a head with a smooth, generally hemispherical, medio-proximally directed, articulating surface, a generally abrupt, distally directed truncation thereto, and a stem trunion-receiving cup in the truncation; and a stem attachable to the head, which stem has intracarpal spike-like distal end, and a proximally directed trunion, which trunion is insertable into the stem trunion-receiving cup of the head. Other digits may be provided with analogous implants, particularly with respect to those digital implants amenable to modularity.

Description

[0001]This is a divisional of application Ser. No. 09 / 352,472 filed on Jul. 14, 1999 A.D.BACKGROUND TO THE INVENTION[0002]I. Field and Purview of the Invention[0003]The present invention concerns in particular a one-piece or a modular basal thumb joint implant for the trapeziometacarpal joint, and can also include an extension of the concept of modularity to other digital joints. The implant generally includes head and stem portions, and it has one or more of the following: a generally acute head-stem attachment orientation; a flanged cross-sectional stem profile; an inwardly curved stem; and an eccentric head attachment site for the stem.[0004]II. Prior Art, and Discovered Problems[0005]Cases of degenerative or post-traumatic arthritis of the trapeziometacarpal joint are known to leave the joint unstable, disfunctional, and painful. In addressing this problem, the Swanson Basal Thumb Joint was developed for use as an adjunct to resection arthroplasty of the joint. The Swanson impla...

AI Technical Summary

Benefits of technology

[0014]Significantly, by the invention, problems in the art are ameliorated if not overcome. The inward (varus) curve of the stem proximally and the eccentric medial placement of the head on the stem avoid the propensity for dislocation of the replaced joint. This anatomically oriented arrangement also permits an unobstructed range of normal pain free motion. The anatomic stem curvature in conjunction with the flanged cross-sectional stem profile, which preferably is a tri-flanged cross-sectional stem profile, provides for a more precise fit with the metacarpal medullary canal anatomy, hence preserving bone stock and assuring optimal long term stability, including near if not complete immovability with respect to rotation, of the implant. The “mix and match” modularity of variably sized heads and stems allows for selective assembly of a composite implant which 1) provides a precise fit for both parts, head and stem, and 2) reduces the on-the-shelf inventory of the composite implant, which, in turn, reduces the cost of the procedure.

Problems solved by technology

Cases of degenerative or post-traumatic arthritis of the trapeziometacarpal joint are known to leave the joint unstable, disfunctional, and painful.

Problems with the foregoing, however, have been discovered to include 1) the straight, non-anatomical countour of the stem, which (a) reduces the rotational stability of the implant, and (b) induces outward mechanical leveraging of the prosthetic head and the proclivity for lateral dislocation of the replaced joint; 2) the demonstrated inferior tribological characteristics of an articulating titanium surface; and 3) the one-piece construction or non-modularity of the implant, which precludes an ability to “mix and match” component parts, consequently requiring a redundant and costly on-the-shelf inventory of implants to assure the availability of an implant which will provide an appropriate head-stem combination that will produce a precise, individualized dimensional fit of both the head and the intramedullary stem parts of the prosthesis.

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